Proppants with improved dust control

ABSTRACT

Provided are proppants for use in hydraulic fracturing operations. The proppants comprise particles having coatings disposed on them as described herein. The proppants exhibit reduced dust generation, for instance during transloading, conveying and/or offloading of the proppant at a wellsite and/or at intermediate shipping transload points.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC § 371 national phase filing ofPCT/US2014/064286 filed Nov. 6, 2014, which claims priority from U.S.provisional application Ser. No. 61/904,619, filed Nov. 15, 2013, andfrom U.S. provisional application Ser. No. 62/021,350, filed Jul. 7,2014, each of which is incorporated herein by reference in its entirety.

FIELD

This invention relates generally to proppants for use in hydraulicfracturing operations. More specifically, the invention relates toproppants coated with a polymer as described herein and methods of theirpreparation and use. The coated proppants provide improved dust control.

BACKGROUND

Hydraulic fracturing is a term that has been applied to a variety ofmethods used to stimulate the production of fluids (e.g., oil, naturalgas, brines, etc.) from subterranean formations. In hydraulicfracturing, a fracturing fluid is injected down a wellbore and againstthe face of the formation at a pressure and flow rate at leastsufficient to overcome the overburden pressure and to initiate and/orextend a fracture(s) into the formation. The fracturing fluid usuallycarries a proppant (e.g., 20-40 mesh sand, bauxite, glass beads, etc.)into a fracture which keeps the formation from closing back down uponitself when the pressure is released. The proppant-filled fracturesprovide permeable channels through which the formation fluids can flowto the wellbore and thereafter be withdrawn.

When preparing, transporting, and/or handling proppant for use inhydraulic fracturing, large amounts of dust, such as silica dust andother proppant dust, may be created by the movement of the proppants.This dust can produce potentially detrimental effects, such as damagingequipment on the hydraulic fracturing site.

Alternative solutions that minimize dust during handling, such asspraying the proppant with moisture, an oil or a coating, typicallyrequire high use levels of such materials, which can detrimentally causethe proppant particles to adhere to one another or behave cohesively,resulting in flowability problems.

The problem addressed by this invention is the provision of newtechnologies that limit the generation of dust from proppants.

STATEMENT OF INVENTION

We have now found that coating of proppant particles with a polymerbinder as described herein is effective at significantly reducing thegeneration of dust from proppants, for instance dust formed duringconveying, transloading and offloading of the proppant at a wellsite andat intermediate shipping transload points. For instance, proppants ofthe invention may result in 70 percent by volume or less, preferably 50percent by volume or less, more preferably 30 percent by volume or less,even more preferably 10 percent by volume or less, of airborne dustcompared to uncoated particles.

In one aspect, therefore, there is provided a proppant for use inhydraulic fracturing comprising: a particle; and a coating disposed onthe particle that is formed from an aqueous coating composition, thecoating composition comprising from 2 to 65 weight percent of asurfactant, and from 1 to 35 weight percent of a polymer binder, andbalance water, based on the total weight of the aqueous coatingcomposition.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph comparing particle size versus volumes for variousuntreated and treated proppant particles.

DETAILED DESCRIPTION

Unless otherwise indicated, numeric ranges, for instance as in “from 2to 10,” are inclusive of the numbers defining the range (e.g., 2 and10).

Unless otherwise indicated, ratios, percentages, parts, and the like areby weight.

Ethyleneoxy (C₂H₄O) refers to —CH₂—CH₂—O—, propyleneoxy (C₃H₆O) refersto —CH₂—CH(CH₃)—O— or —CH(CH₃)—CH₂—O—, and butyleneoxy (C₄H₈O) refers to—CH₂—CH(CH₂CH₃)—O— or —CH(CH₂CH₃)—CH₂—O—.

“(Meth)acrylate” as used herein means acrylate, methacrylate, ormixtures thereof, “(meth)acrylic” means acrylic, methacrylic, ormixtures thereof, and the term “(meth)acrylamide” means acrylamide,methacrylamide, or mixtures thereof.

Dust means particles as described herein that are less than 125 micronsor that pass through a 120 mesh sieve.

The invention provides a proppant for use in hydraulic fracturingoperations (including in manufacturing, storage, transportation, and useactivities associated with hydraulic fracturing). The proppant comprisesa particle and a coating disposed on the particle.

The particle may be any such material that is suitable for use in ahydraulic fracturing or similar processes. Examples of suitableparticles include, without limitation, minerals, silica sand, quartz,ceramics such as synthetic ceramic particles, or combinations thereof.

A preferred particle that is commonly used as a proppant is silica sandor silicon dioxide (SiO₂) sand, known colloquially in the industry as“frac sand.” Preferably, frac sands are those from high silica (quartz)sandstones or unconsolidated deposits. The particles may containnon-silica impurities, such as calcium, magnesium, iron, mixturesthereof, etc. The particles to be coated may be of any shape, althoughpreferably they are roughly spherical.

The particle may generally be of any suitable grain size. In someembodiments, the particle may have a grain size ranging from 12 to 140mesh, alternatively 20 to 70 mesh, and may include standard sizes suchas 12 to 20 mesh, 16 to 30 mesh, 20 to 40 mesh, 30 to 50 mesh, and 40 to70 mesh, whereby 90% of the product falls between the designated sievesizes. Some specific examples are 8/12, 10/20, 20/40, and 70/140. Meshsize of particles may be determined from the percentage of particlesthat are retained by a series of mesh sieves having certain-sizedopenings. In a mesh size number, the mesh number designates the nominalnumber of holes in a standard unit area. Thus the small number is thelarger particle size while the larger number is the small particle sizein that category. The smaller the number, the coarser the grain. Grainsize can also be measured using standard length measurements such asmillimeters or micrometers, with some examples being grain size rangesof 2.38-1.68 mm, 2.00-0.84 mm, 0.84-0.42 mm, and 210-105 micrometers.While any particle size sample may be predominantly sized in the rangesindicated above, small portions (e.g., less than 5%) of the particlesize distribution of any sample may be either larger or smaller than theranges indicated, either due to shape irregularities or physicalaffinity of small particles clinging to larger particles due toelectrostatics or other reasons.

According to the invention, the particle has a coating disposed on itthat is formed from an aqueous coating composition as described below.The term “disposed” means that the coating covers the exterior of theparticle and includes both partial and complete covering of the particleby the coating. The particle on which the coating of the invention isdisposed may optionally be pre-coated (such as with a resin) orpre-treated, such as described, for instance, in U.S. Pre-Grantpublication 2010/0179077 and U.S. Pat. No. 7,270,879, each of which isincorporated herein by reference. In such instances, the coating of theinvention is disposed on the pre-coated or pre-treated particle.

In a some embodiments, the coating covers less than 50 percent of theparticle, alternatively less than 40 percent, alternatively less than 30percent, alternatively less than 20 percent, or alternatively less than10 percent of the particle. Even with these incomplete coverings, theadhesive nature of the coating attracts the dust to the selected coatedareas on the particle and binds them to the particle. Coverage level canbe determined by various techniques, such as scanning electronicmicroscopy and atomic mapping.

The aqueous coating composition used for coating the particle in theinvention comprises a surfactant, a polymer binder, and water.

The surfactant may be a nonionic, cationic, or anionic material, and itmay be a blend of surfactants. Non-limiting examples of surfactantsknown in the art that may suitably be used include those described inU.S. Pre-Grant publication 2002/0045559 which is incorporated herein byreference.

Suitable anionic surfactants may include, for instance, an sulfonic acidsurfactant, such as a linear alkyl benzene sulfonic acid, or saltthereof. Anionic sulfonate or sulfonic acid surfactants suitable for useherein include the acid and salt forms of C₅-C₂₀, more preferably aC₁₀-C₁₆, more preferably a C₁₁-C₁₃ alkylbenzene sulfonates, alkyl estersulfonates, C₆-C₂₂ primary or secondary alkane sulfonates, sulfonatedpolycarboxylic acids, and any mixtures thereof, but preferably C₁₁-C₁₃alkylbenzene sulfonates. Anionic sulfate salts or acids surfactantsinclude the primary and secondary alkyl sulfates, having a linear orbranched alkyl or alkenyl moiety having from 9 to 22 carbon atoms ormore preferably C₁₂ to C₁₈ alkyl.

Anionic surfactants that may be used also include beta-branched alkylsulfate surfactants or mixtures of commercially available materials,having a weight average (of the surfactant or the mixture) branchingdegree of at least 50% or even at least 60% or even at least 80% or evenat least 95%. Mid-chain branched alkyl sulfates or sulfonates are alsosuitable anionic surfactants for use in the invention. Preferred are themid-chain branched alkyl sulfates.

Suitable mono-methyl branched primary alkyl sulfates that may be used inthe invention include those selected from the group consisting of:3-methyl pentadecanol sulfate, 4-methyl pentadecanol sulfate, 5-methylpentadecanol sulfate, 6-methyl pentadecanol sulfate, 7-methylpentadecanol sulfate, 8-methyl pentadecanol sulfate, 9-methylpentadecanol sulfate, 10-methyl pentadecanol sulfate, 11-methylpentadecanol sulfate, 12-methyl pentadecanol sulfate, 13-methylpentadecanol sulfate, 3-methyl hexadecanol sulfate, 4-methyl hexadecanolsulfate, 5-methyl hexadecanol sulfate, 6-methyl hexadecanol sulfate,7-methyl hexadecanol sulfate, 8-methyl hexadecanol sulfate, 9-methylhexadecanol sulfate, 10-methyl hexadecanol sulfate, 11-methylhexadecanol sulfate, 12-methyl hexadecanol sulfate, 13-methylhexadecanol sulfate, 14-methyl hexadecanol sulfate, and mixturesthereof.

Suitable di-methyl branched primary alkyl sulfates may include materialsselected from the group consisting of: 2,3-methyl tetradecanol sulfate,2,4-methyl tetradecanol sulfate, 2,5-methyl tetradecanol sulfate,2,6-methyl tetradecanol sulfate, 2,7-methyl tetradecanol sulfate,2,8-methyl tetradecanol sulfate, 2,9-methyl tetradecanol sulfate,2,10-methyl tetradecanol sulfate, 2,1-methyl tetradecanol sulfate,2,12-methyl tetradecanol sulfate, 2,3-methyl pentadecanol sulfate,2,4-methyl pentadecanol sulfate, 2,5-methyl pentadecanol sulfate,2,6-methyl pentadecanol sulfate, 2,7-methyl pentadecanol sulfate,2,8-methyl pentadecanol sulfate, 2,9-methyl pentadecanol sulfate,2,10-methyl pentadecanol sulfate, 2,11-methyl pentadecanol sulfate,2,12-methyl pentadecanol sulfate, 2,13-methyl pentadecanol sulfate, andmixtures thereof.

Examples of cationic surfactants that may be used in the inventioninclude cationic mono-alkoxylated and bis-alkoxylated quaternary aminesurfactants with a C 6-C18 N-alkyl chain, such as of the generalformula:

wherein R1 is an alkyl or alkenyl moiety containing from about 6 toabout 18 carbon atoms, preferably 6 to about 16 carbon atoms, mostpreferably from about 6 to about 14 carbon atoms; R2 and R3 are eachindependently alkyl groups containing from one to about three carbonatoms, preferably methyl, most preferably both R2 and R3 are methylgroups; R4 is selected from hydrogen (preferred), methyl and ethyl; X isan anion such as chloride, bromide, methylsulfate, sulfate, or the like,to provide electrical neutrality; A is a alkoxy group, especially aethyleneoxy, propyleneoxy or butyleneoxy group; and p is from 0 to about30, preferably 2 to about 15, most preferably 2 to about 8.

The cationic bis-alkoxylated amine surfactant preferably has the generalformula:

wherein R1 is an alkyl or alkenyl moiety containing from about 8 toabout 18 carbon atoms, preferably 10 to about 16 carbon atoms, mostpreferably from about 10 to about 14 carbon atoms; R2 is an alkyl groupcontaining from one to three carbon atoms, preferably methyl; R3 and R4can vary independently and are selected from hydrogen (preferred),methyl and ethyl, X— is an anion such as chloride, bromide,methylsulfate, sulfate, or the like, sufficient to provide electricalneutrality. A and A′ can vary independently and are each selected fromC1-C4 alkoxy, especially ethyleneoxy, propyleneoxy, butyleneoxy andmixtures thereof; p is from 1 to about 30, preferably 1 to about 4 and qis from 1 to about 30, preferably 1 to about 4, and most preferably bothp and q are 1.

Another suitable group of cationic surfactants which can be used in theinvention are cationic ester surfactants. Suitable cationic estersurfactants, including choline ester surfactants, have for example beendisclosed in U.S. Pat. Nos. 4,228,042, 4,239,660 and 4,260,529.

In the invention, nonionic surfactants are preferred (including blendsthereof). Suitable nonionic surfactants include, for instance,alkoxylate materials including those that are derived from ethyleneoxide, propylene oxide, and/or butylene oxide. Examples are described,for instance, in U.S. Pat. No. 7,906,474 and U.S. Pre-Grant publication2011/0098492, each of which is incorporated herein by reference.

In some embodiments, the surfactant for use in the invention is anonionic alkoxylate of the formula I:R_(a)O-(AO)_(z)—H  (I)wherein R_(a) is aryl (e.g., phenyl), or linear or branched C₆-C₂₄alkyl, AO at each occurrence is independently ethyleneoxy, propyleneoxy,butyleneoxy, or random or block mixtures thereof, and z is from 1 to 50.

In some embodiments, a preferred nonionic surfactant for use in theaqueous coating composition is an alkoxylate represented by thefollowing formula II:R—O—(C₃H₆O)_(x)(C₂H₄O)_(y)—H  (II)wherein x is a real number within a range of from 0.5 to 10; y is a realnumber within a range of from 2 to 20, and R represents a mixture of twoor more linear alkyl moieties each containing one or more linear alkylgroup with an even number of carbon atoms from 4 to 20. One of theadvantages of surfactants of formula I, particularly those that arenatural source derived, as described below, is their generalbiodegradability and low toxicity.

Formula II surfactants are preferably prepared in a sequential mannerthat includes propoxylation (adding PO or poly(oxypropylene)) moietiesto an alcohol or mixture of alcohols to form a PO block followed byethoxylation (adding EO or poly(oxyethylene)) moieties to form an EOblock attached to the PO block, but spaced apart from R which representsalkyl moieties from the alcohol or mixture of alcohols. One may eitherbegin with a mixture of alcohols that provides a distribution of alkylmoieties and then sequentially propoxylate and ethoxylate the mixture orseparately propoxylate and ethoxylate select alcohols and then combinesuch alkoxylates (propoxylated and ethoxylated alcohols) in proportionssufficient to provide a distribution, for example, as shown in Table Abelow.

Preferably, R represents a mixture of linear alkyl moieties that are thealkyl portions of seed oil-derived alcohols. In some embodiments, R hasan alkyl moiety distribution as in Table A:

TABLE A Amount Alkyl Moieties  0 wt % to 40 wt % C₆ 20 wt %-40 wt % C₈20 wt %-45 wt % C₁₀ 10 wt %-45 wt % C₁₂  0 wt % to 40 wt % C₁₄  0 wt %to 15 wt % C₁₆₋₁₈ As used herein, “C₁₆₋₁₈” means “C₁₆, C₁₈, or a mixturethereof.”

Any one or more of C₆, C₁₄, and C₁₆₋₁₈ alkyl moieties may, but need notbe, present in the present invention. When present, the amounts of C₆,C₁₄, and C₁₆₋₁₈ alkyl moieties may satisfy any of their respectiveranges as shown in Table A as long as all weight percentages total 100wt %. In some embodiments, one or more of C₆, C₁₄, and C₁₆₋₁₈ alkylmoieties are present in an amount greater than zero. In someembodiments, C₆ and C₁₄ are each present in an amount greater than zero,and there is also an amount greater than zero of C₁₆₋₁₈.

In some embodiments, R has an alkyl moiety distribution as in Table B.

TABLE B Amount Alkyl Moieties  0 wt % to 36 wt % C₆ 22 wt %-40 wt % C₈27 wt %-44 wt % C₁₀ 14 wt %-35 wt % C₁₂  5 wt % to 13 wt % C₁₄  0 wt %to 5 wt % C₁₆₋₁₈

The surfactant mixture as in Table B includes a mixture of at least fouralkyl moieties: C₈, C₁₀, C₁₂, and C₁₄. Any one or more of C₆ and C₁₆₋₁₈alkyl moieties may, but need not be, present in surfactant compositionsof this preferred subset of the preferred surfactants. When present, theamounts of C₆, and C₁₆₋₁₈ alkyl moieties may satisfy any of theirrespective ranges as shown in Table A as long as all weight percentagestotal 100 wt %.

In some embodiments, the amount of C₆ in R is zero. Independently, insome embodiments, the amount of C₁₆₋₁₈ in R is not zero.

Formula II above includes variables “x” and “y” that, taken together,establish a degree of alkoxylation in an oligomer distribution.Individually, “x” and “y” represent average degrees of, respectively,propoxylation and ethoxylation. In some embodiments, the degree ofpropoxylation or “x” falls within a range of from 0.5 to 7, preferablywithin a range of 0.5 to less than 4, more preferably within a range offrom 0.5 to 3, still more preferably within a range of from 2 to 3, andeven more preferably within a range of from 2.5 to 3. The degree ofethoxylation or “y” preferably falls within a range of from 2 to 10,more preferably within a range of from 2 to 8, still more preferablywithin a range of from 4 to 8 and even more preferably within a range offrom 6 to 8.

In some embodiments, the sum of x and y is 1 to 15. In some embodiments,the sum of x and y is 1 to 7. Independently, in some embodiments, y isgreater than x. In some embodiments, y is greater than or equal to 2times x. In some embodiments, x is within a range of from 2.5 to 3, y iswithin a range of from 2 to 10, and R has an alkyl moiety distributionas in Table B. In some embodiments, the amount of C₆ in R is zero, theamount of C₁₆₋₁₈ in R is not zero, and the sum of x and y is 1 to 7.

In some embodiments, the formula II surfactant is C₈₋₁₆O(PO)_(2.5)(EO)₅H(based on raw material feeds) derived from an alcohol stream thatprovides an alkyl moiety weight percentage distribution as follows:C₈=22.5%, C₁₀=27.5%, C₁₂=35%, C₁₄=12.5 and C₁₆=2.5%.

In some embodiments, the formula II surfactant is a blend ofC₈₋₁₀O(PO)_(2.5)(EO)_(5.8)H (derived from an alcohol blend consisting ofabout 55% n-decanol and about 45% n-octanol) and C₁₂₋₁₆O(PO)_(2.5)(EO)₈H(derived from an alcohol blend consisting of about 70% n-dodecanol, 25%n-tetradecanol and 5% n-hexadecanol), preferably at a ratio of the twoformula II materials of 65:35.

In some embodiments, the surfactant for use in the aqueous coatingcomposition of the invention is an alkoxylate of the formula III:R¹O—(CH₂CH(R²)—O)_(p)—(CH₂CH₂O)_(q)—H  (III)wherein R¹ is linear or branched C₄-C₁₈ alkyl; R² is CH₃ or CH₃CH₂; p isa real number from 0 to 11; and q is a real number from 1 to 20. In someembodiments, R¹ in formula III is linear or branched C₆-C₁₆ alkyl,alternatively linear or branched C₈-C₁₄ alkyl, alternatively linear orbranched C₆-C₁₂ alkyl, alternatively linear or branched C₆-C₁₀ alkyl,alternatively linear or branched C₈-C₁₀ alkyl. In some embodiments, R¹is linear or branched C8 alkyl. In some embodiments, R¹ is 2-ethylhexyl(CH₃CH₂CH₂CH₂CH(CH₂CH₃)CH₂—). In some embodiments, R¹ is 2-propylheptyl(CH₃CH₂CH₂CH₂CH₂CH(CH₂CH₂CH₃)CH₂—). In some embodiments, R² in formulaIII is CH₃. In some embodiments, R² is CH₃CH₂. In some embodiments, p informula III is from 3 to 10, alternatively from 4 to 6. In someembodiments, q in formula III is from 1 to 11, alternatively from 3 to11.

In some embodiments, the formula III surfactant isC₈-C₁₄O—(PO)₂₋₅(EO)₅₋₉—H, where the C8-C14 group is linear or branched,preferably branched. In some embodiments, the formula III surfactant is2EH(PO)₂(EO)₄—H, 2EH(PO)₃(EO)_(6.8)—H, 2EH(PO)_(5.5)(EO)₈—H,2EH(PO)₉(EO)₉—H, 2EH(PO)₁₁(EO)₁₁—H, 2EH(PO)₅(EO)₃—H, or 2EH(PO)₅(EO)₆—H(2EH=2-ethylhexyl).

In some embodiments, the surfactant for use in the aqueous coatingcomposition is an alkoxylate of the formula IV:R_(a)—O—(C₂H₄O)_(m)(C₄H₈O)_(n)—H  (IV)wherein R_(a) is one or more independently straight chain or branchedalkyl groups or alkenyl groups having 3-22 carbon atoms, m is from 1 to12, and n is from 1 to 8. In some embodiments, m may be from 2 to 12, orfrom 2 to 10, or even from 5-12. In some embodiments, n may be from 2 to8, or even from 3-8, or even from 5 to 8.

In some embodiments, the surfactant for use in the aqueous coatingcomposition is an alkoxylate of the formula V:C₄H₉O—(C₂H₄O)_(r)(C₃H₉O)_(s)(C₂H₄O)t—H  (V)wherein r is from 3-10, s is from 3 to 40, and t is from 10 to 45.

In some embodiments, the surfactant is an alkoxylate of the formula VI:R—O—(—CH—CH₃—CH₂—O—)_(x)—(—CH₂—CH₂—O—)_(y)—H  (VI)wherein x is from 0.5 to 10, y is from 2 to 20, and R is a mixture oftwo or more linear alkyl moieties having an even number of carbon atomsbetween 4 and 20.

In some embodiments, the surfactant for use in the aqueous coatingcomposition is an alkyl polyglucoside of the formula:

wherein m is from 1 to 10 and n is from 3 to 20.

In some embodiments, the surfactant is present in the aqueous coatingcomposition of the invention at a concentration of from 2 to 65 weightpercent, preferably from 5 to 50 weight percent, based on the totalweight of the aqueous composition.

The aqueous coating composition used in the invention may optionallycomprises a flocculant. Suitable flocculants include, withoutlimitation, a water soluble poly(ethylene oxide) resin or an acrylamideresin (e.g., Hydrolyzed Poly-Acrylamide, “HPAM”) or other flocculatingagent.

Poly(ethylene oxide) (“PEO”) resins, optionally used in the invention,comprise polymerized units derived from ethylene oxide. They may alsocomprise units derived from other monomers such as propylene oxide, inaddition to ethylene oxide. The poly(ethylene oxide) resins aregenerally soluble in water and provide essentially clear, homogeneouscompositions when dispersed in water.

In some embodiments, water soluble poly(ethylene oxide) resins suitablefor use in the invention have the general formula HO —[—CH₂CH₂O—]_(n)—H,wherein n is from 1,000 to 200,000, for example, 1,000-100,000, or even1,000 to 50,000. The poly(ethylene oxide) resins may have a solubilityin water of from 0.01% to 100%, preferably 0.02% to 5%, at 20° C. andatmospheric pressure. Furthermore, in some embodiments, suitable watersoluble poly(ethylene oxide) resins have a weight average molecularweight, MW_(w), of 50,000 to 8,000,0000 grams per mole (g/mol), such as75,000 to 4,000,000 g/mol, or even 100,000 to 1,000,000 g/mol. Optionalflocculants, such as poly(ethylene oxide) resins, may be readilyprepared using known methods. In addition, they are also commerciallyavailable.

In some embodiments, the flocculant, if used, is present in the aqueouscoating composition of the invention at a concentration of from 0.01 to5 weight percent, preferably from 0.02 to 2, based on the total weightof the aqueous composition.

Aqueous coating compositions in accordance with the invention alsocomprise a film-forming or binder polymer (including blends thereof),generally in the form of an aqueous dispersion or emulsion. Polymerbinders suitable for use in the invention typically have glasstransition temperatures, T_(g), from −40 to 120° C., such as from −20°C. to 90° C., or from −15° C. to 80° C., or even from −10° C. to 75° C.The “glass transition temperature,” or “T_(g),” as used herein, meansthe temperature at or above which a glassy polymer will undergosegmental motion of the polymer chain. Glass transition temperatures ofa polymer can be estimated by the Fox Equation (Bulletin of AmericanPhysics Society, 1 (3), p 123, 1956), as follows:1/T _(g) =w ₁ /T _(g,1) +w ₂ /T _(g,2)

For a copolymer comprising two type of monomers, w₁ and w₂ refer to theweight fraction of the two monomers, and T_(g,1) and T_(g,2) refer tothe glass transition temperatures of the two corresponding homopolymersmade from the monomers. For polymers containing three or more monomers,additional terms are added (w_(n)/T_(g,n)). The T_(g) of a polymer canalso be measured by various techniques including, for example,differential scanning calorimetry (DSC).

Polymer binders suitable for use in the aqueous coating compositions arepreferably water insoluble emulsion polymers derived from one or moreethylenically unsaturated monomers, typically in the form of an aqueousdispersion. Suitable ethylenically unsaturated monomers includeethylenically unsaturated carboxylic acids, such as (meth)acrylic acid,derivatives thereof, such as (C₁-C₂₀)alkyl (meth)acrylate esters and(meth)acrylamide, vinyl aromatic monomers, vinyl alkyl monomers, alphaolefins, and combinations thereof. Further examples of suitable monomersinclude, without limitation, methyl acrylate, ethyl acrylate, propylacrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate,secondary butyl acrylate, tertiary-butyl acrylate, methyl methacrylate,ethyl methacrylate, propyl methacrylate, isopropyl methacrylate,cyclopropyl, methacrylate, butyl methacrylate and isobutyl methacrylate,hexyl and cyclohexyl methacrylate, cyclohexyl acrylate, isobornylmethacrylate, 2-ethylhexyl acrylate (EHA), 2-ethylhexyl methacrylate,octyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate,undecyl (meth)acrylate, dodecyl (meth)acrylate (also known as lauryl(meth)acrylate), tridecyl (meth)acrylate, tetradecyl (meth)acrylate(also known as myristyl (meth)acrylate), pentadecyl (meth)acrylate,hexadecyl (meth)acrylate (also known as cetyl (meth)acrylate),heptadecyl (meth)acrylate, octadecyl (meth)acrylate (also known asstearyl (meth)acrylate), nonadecyl (meth)acrylate, eicosyl(meth)acrylate, hydroxyethyl methacrylate, styrene, alpha-methyl styreneand substituted styrenes, such as vinyl toluene, 2-bromostyrene,4-chlorostyrene, 2-methoxystyrene, 4-methoxystyrene, alpha-cyanostyrene,allyl phenyl ether and allyl tolyl ether, ethylene, propylene, butene,hexene, octane, decene, vinyl acetate (optionally copolymerized with anacrylate, such as butyl acrylate, or with ethylene), and combinationsthereof. Preferred monomers include methyl acrylate, ethyl acrylate,butyl acrylate and 2-ethylhexyl acrylate, optionally in combination witha vinyl aromatic monomer, preferably styrene. More preferred is butylacrylate optionally in combination with a vinyl aromatic monomer,preferably styrene.

Further examples include, without limitation, ethylenically unsaturated(C₃-C₉) carboxylic acid monomers, such as unsaturated monocarboxylic anddicarboxylic acid monomers. For example, unsaturated monocarboxylicacids include acrylic acid (AA), methacrylic acid (MAA),alpha-ethacrylic acid, beta-dimethylacrylic acid, vinylacetic acid,allylacetic acid, ethylidineacetic acid, propylidineacetic acid,crotonic acid, acryloxypropionic acid and alkali and metal saltsthereof. Suitable unsaturated dicarboxylic acid monomers include, forexample, maleic acid, maleic anhydride, fumaric acid, itaconic acid,citraconic acid, mesaconic acid, or methylenemalonic acid. Methacrylicacid (MAA) is a preferred ethylenically unsaturated carboxylic acid.

Other unsaturated monomers that, when used, are preferably copolymerizedwith one or more of the foregoing alkyl (meth)acrylates include, withoutlimitation, butadiene, acrylonitrile, methacrylonitrile, crotononitrile,alpha-chloroacrylonitrile, ethyl vinyl ether, isopropyl vinyl ether,isobutyl vinyl ether, butyl vinyl ether, diethylene glycol vinyl ether,decyl vinyl ether, ethylene, methyl vinyl thioether and propyl vinylthioether, esters of vinyl alcohol, and combinations thereof.

In some embodiments, the polymer binder is an aqueous dispersion ofpolymer units derived from, based on the weight of the polymer: i) from90 to 99.9 weight percent of at least one ethylenically unsaturatedmonomer not including component ii; and ii) from 0.1 to 10 weightpercent of (meth)acrylamide. In some embodiments, the monomer of i)comprises a (C₁-C₂₀)alkyl (meth)acrylate ester in combination with avinyl aromatic monomer. In some embodiments, i) is butyl acrylate incombination with styrene. Preferably, the amount of butyl acrylate insuch combination may be from 5 to 90 weight percent and the amount ofstyrene may be from 95 to 10 weight percent based on the total weight ofthe butyl acrylate and styrene.

In some embodiments of the invention, the polymer binder is an aqueousdispersion of polymer units derived from: butyl acrylate, styrene, andacrylamide. Preferably, the amounts, based on the weight of the polymerare: from 65 to 75 weight percent of butyl acrylate; from 23 to 33weight percent of styrene; and from 0.5 to 6 weight percent ofacrylamide. More preferably, the amounts, based on the weight of thepolymer are: from 69 to 71 weight percent of butyl acrylate; from 27 to29 weight percent of styrene; and from 1 to 3 weight percent ofacrylamide.

In some embodiments of the invention, the polymer binder is an aqueousdispersion of polymer units derived from: butyl acrylate, styrene,hydroxyethyl methacrylate, and acrylamide. Preferably, the amounts,based on the weight of the polymer are: from 65 to 75 weight percent ofbutyl acrylate; from 24 to 32 weight percent of styrene; from 0.25 to 2weight percent hydroxyethyl methacrylate; and from 0.5 to 6 weightpercent of acrylamide. More preferably, the amounts, based on the weightof the polymer are: from 69 to 71 weight percent of butyl acrylate; from26 to 28 weight percent of styrene; from 0.25 to 0.75 weight percenthydroxyethyl methacrylate; and from 1 to 3 weight percent of acrylamide.

In some embodiments, the polymer binder is an aqueous dispersion ofpolymer units derived from, based on the weight of the polymer: i) from80 to 99.9 weight percent of at least one ethylenically unsaturatedmonomer not including component ii); and ii) from 0.1 to 20 weightpercent of a carboxylic acid monomer. Suitable carboxylic acid monomersinclude those described above. Methacrylic acid (MAA) is preferred.

In some embodiments, the polymer binder used in the composition of theinvention is a metal-crosslinked emulsion copolymer, such as thosedescribed in U.S. Pat. Nos. 4,150,005, 4,517,330, and U.S. Pre-Grantpublications 2011/0118409, and 2011/0230612, each of which isincorporated herein by reference. Suitable metal crosslinkedfilm-forming emulsion (co)polymers comprise polymer units derived fromone or more ethylenically unsaturated monomers and one or more acidfunctionalized monomers reacted with a polyvalent metal compound at atemperature above or below the T_(g) of the acid functionalized polymerto produce a crosslinked polymer.

In some embodiments, the metal-crosslinked copolymer is derived from,based on the weight of the copolymer: i) from 75 to 99 weight percent ofat least one ethylenically unsaturated monomer not including componentii; and ii) from 1 to 25 weight percent of an ethylenically unsaturatedcarboxylic acid monomer stabilized with a polyvalent metal. In someembodiments, the monomer of i) comprises one or more (C₁-C₂₀)alkyl(meth)acrylate esters. In some embodiments, the monomer of i) comprisesone or more (C₁-C₂₀)alkyl (meth)acrylate esters optionally incombination with a vinyl aromatic monomer. In some embodiments, i) isbutyl acrylate, methylmethacrylate, and styrene. Preferably, the amountof butyl acrylate in such combination is from 1 to 80, the amount ofmethylmethacrylate is from 5 to 70, and the amount of styrene is from 0to 70 weight percent based on the total weight of the butyl acrylate,methylmethacrylate and styrene.

Suitable carboxylic acid monomers for the foregoing embodiment include,without limitation, those described above. Methacrylic acid (MAA) ispreferred.

The polyvalent metal crosslinker employed in the foregoing embodimentsis generally in the form of a polyvalent metal complex containing thepolyvalent metal moiety, an organic ligand moiety and, if thecrosslinker is added as a chelate to the formulation in solubilizedform, an alkaline moiety. The polyvalent metal ion may be that ofberyllium, cadmium, copper, calcium, magnesium, zinc, zirconium, barium,aluminum, bismuth, antimony, lead, cobalt, iron, nickel or any otherpolyvalent metal which can be added to the composition by means of anoxide, hydroxide, or basic, acidic or neutral salt which has anappreciable solubility in water, such as at least about 1% by weighttherein. The alkaline moiety may be provided by ammonia or an amine. Theorganic ligand may be ammonia or an amine or an organic bidentate aminoacid. The amino acid bidentate ligand is preferably an aliphatic aminoacid, but may also be a heterocyclic amino acid. Preferred polyvalentmetal complexes include the diammonium zinc (II) and tetra-ammonium zinc(II) ions, cadmium glycinate, nickel glycinate, zinc glycinate,zirconium glycinate, zinc alanate, copper beta-alanate, zincbeta-alanate, zinc valanate, copper bisdimethylamino acetate.

The amount of polyvalent metal compound added is preferably from about15% to 100% of the equivalent of the acid residues of the copolymeremulsion, and may be at least about 15%. More preferably the amount ofthe polyvalent metal ionic crosslinking agent is from about 35% to 80%of the equivalent of the acid residues of the copolymer emulsion. Stillmore preferably the amount of the polyvalent metal crosslinking agent isfrom about 40% to 70% of the equivalent of the acid residues.

In some embodiments of the invention, the metal-crosslinked copolymer isderived from butyl acrylate, methyl methacrylate, styrene, hydroxy ethylmethacrylate, acrylic acid, and methacrylic acid, crosslinked with zincion. Preferably, the amounts, based on the weight of the copolymer, are:from 28 to 40 weight percent butyl acrylate, from 5 to 20 weight percentmethyl methacrylate, from 35 to 45 weight percent styrene, from 1 to 10weight percent hydroxy ethyl methacrylate, from 1 to 10 weight percentacrylic acid and from 1 to 10 weight percent methacrylic acid,crosslinked with zinc ion. More preferably, the amounts, based on theweight of the copolymer, are: from 29 to 31 weight percent butylacrylate, from 15 to 17 weight percent methyl methacrylate, from 39 to41 weight percent styrene, from 4 to 6 weight percent hydroxy ethylmethacrylate, from 4 to 6 weight percent acrylic acid and from 4 to 6weight percent methacrylic acid, crosslinked with zinc ion (about 0.9equivalents).

In further embodiments, the polymer binder is a copolymer of a vinylaromatic monomer such as styrene, o-methyl styrene, p-methyl styrene, ort-butylstyrene and a diene monomer, such as butadiene or isoprene.Preferred such binders are copolymers of styrene and butadiene. In someembodiments, the weight ratio of styrene to butadiene in the copolymerranges from 70:30 to 30:70.

Methods for preparation of water insoluble polymer binders suitable foruse in the composition of the invention are known in the art and notespecially limited. The preparation method may be selected fromsolution, dispersion and emulsion polymerization processes. Emulsionpolymerization is especially useful for preparing suitable polymerbinders. The practice of emulsion polymerization is well known anddiscussed in detail in the literature, for example, in D. C. Blackley,Emulsion Polymerization (Wiley, 1975). The polymerization temperature istypically from ambient temperature up to 90° C. and may also involve useof dispersing agents, initiators, accelerators, emulsifiers, chaintransfer agents. As will be readily understood by persons of ordinaryskill, dispersing agents may include anionic or nonionic dispersingagents, polymerization initiators may be of the free radical type, suchas ammonium or potassium persulfate. The initiators may be used alone orwith an accelerator, such as potassium metabisulfite or sodiumthiosulfate. Examples of suitable emulsifiers include, for example,alkaline metal and ammonium salts of alkyl, aryl, alkaryl and aralkylsulfonates, sulfates, polyether sulfates, and alkoxylated derivatives offatty acids, esters, alcohols, amines, amides and alkylphenols. Chaintransfer agents, including mercaptans, polymercaptans and polyhalogencompounds may be used in the polymerization mixture to control molecularweight of the polymer.

In some embodiments, the polymer binder is present in the aqueouscoating composition of the invention at a concentration of from 1 to 35weight percent, preferably from 5 to 20 weight percent, based on thetotal weight of the aqueous composition (including optional ingredientsas described below).

The aqueous coating compositions for use in the invention may containadditional optional ingredients such as, without limitation, one or moresolvents, preservatives, wetting aids, leveling aids, wax emulsions,defoamers and viscosity modifiers, biocides, among other things.

In some embodiments, the aqueous coating compositions of the inventionoptionally contain a fluorescent dye as an optical brightener.Fluorescent dyes may be used to determine coating uniformity and coatweight. Such use is beneficial because it is a non-destructive techniquethat can give rapid readings of the coating quality without detractingfrom the appearance of the product.

It has surprisingly been discovered that in some embodiments, includingthe optical brighteners described herein in the coating compositionsprovides the added benefit of further suppressing dust from fineparticles. Thus the brightener not only provides an easy way fordetermining the presence of a coating on the particle, but also in someembodiments further enhances dust suppression.

In some embodiments, optical brighteners for use in the invention arecoumarin or coumarin derivatives of the following general structure:

wherein R is H, C1-C12 alkyl, a C3-C12 cycloaliphatic group, a C1-C12alkyl halide group, or a carboxy group; and R² is H, hydroxy (—OH),amine (—NH2), C1-C12 mono- or di-alkylamine, or a mono- ordi-cycloaliphatic amine group.

Preferably, the coumarin or coumarin derivative are selected from thegroup consisting of coumarin, 7-diethylamino-4-methylcoumarin,7-hydroxy-4-methylcoumarin, 7-amino-4-methylcoumarin,{7-(dimethylamino)-2,3-dihydrocyclopenta-[c][1]benzopyran-4(1H)-one},{7-(dimethylamino)-4-(trifluoromethyl)coumarin)},{2,3,6,7-tetrahydro-9-(trifluoromethyl)-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinnolizin-11-one}, coumarin-3-carboxylic acid,3-[2-(diethylamino)ethyl]-7-hydroxy-4-methylcoumarin, anddihydrocoumarin. A particularly preferred coumarin derivative useful inthe present invention is 7-(diethylamino)-4-methylcoumarin, which may berepresented by the following structure:

Other optical brighteners that may be used in the invention include, forinstance, bis-stilbene compounds such as those described in U.S. Pat.No. 3,984,399, bis(benzoxazolyl) thiophene compounds such as thosedescribed in U.S. Pat. No. 3,135,762, and4,4′-bis(2-benzoxazolyl)stilbene compounds such as described in BE651310, each of which is hereby incorporated by reference herein.

More specific examples of suitable optical brighteners include, againwithout limitation,2,2′-[(1,1′-biphenyl)-4,4′-diyldi-2,1-ethenediyl]-bis-benzenesulfonicacid disodium salt, 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene, or4,4′-Bis(2-benzoxazolyl)stilbene.

In some embodiments, it is preferred to dissolve or disperse the opticalbrightener in a solvent prior to addition to coating composition.Hydrophobic solvents are preferred. Examples of suitable solventsinclude, without limitation, 2,2,4-trimethyl-1,3-pentanediolmono(2-methylpropanoate), 1,2-Benzenedicarboxylic acid dibutyl ester, orhexyl cellosolve.

When used, the optical brightener is, in some embodiments, typicallypresent in the aqueous coating composition of the invention at aconcentration of from 0.001 to 5 weight percent, preferably from 0.05 to0.2 weight percent, more preferably from 0.01 to 0.1 weight percent,based on the total weight of the aqueous composition.

The balance of the aqueous compositions, containing surfactant, water,polymer binder, optional poly(ethylene oxide), and any optionalingredients or co-solvents, is water. In some embodiments, the amount ofwater in the aqueous coating composition is 20 weight percent or less,alternatively 18 weight percent or less, or alternatively 16 weightpercent or less, based on the total weight of the coating composition.In some embodiments, the amount of water in the aqueous coatingcomposition is 5 weight percent or more, alternatively 10 weight percentor more, or alternatively 15 weight percent or more, based on the totalweight of the coating composition.

The aqueous coating composition according to the invention may be coatedon the proppant particle using techniques well known to those skilled inthe art. By way of non-limiting example, the particle and the aqueouscoating composition may be blended in a mixer with mechanical agitation.Or the aqueous coating composition may be sprayed onto a moving bed orfalling stream of the particles. Or some combination of spraying thecoating composition onto the particles followed by mixing withmechanical agitation may be used.

Particles may be heated or not. Some coating compositions may benefitfrom higher temperatures to induce some level of crosslinking. Othercoating compositions merely benefit from the more rapid evaporation ofthe emulsifying water from the coating.

There is no particular limitation on how much coating should be appliedto a particle. In some embodiments, it may be preferred that the totalweight of the proppant comprise between about 100 ppm and about 10,000ppm of the coating, on a dry basis. In a preferred embodiment, theamount of coating on the proppant, on a dry basis, is less than 10,000ppm of particle weight, alternatively less than 5,000 ppm of particleweight, alternatively less than 2,000 ppm of particle weight, oralternatively less than 1,000 ppm of particle weight. In anotherpreferred embodiment, the amount of coating on the particle, on a drybasis, is between 300 ppm and 700 ppm of particle weight.

As indicated above, proppant particles as described herein may exhibitsignificantly reduced dust generation, for instance during transloadingand offloading of the proppant at a wellsite and/or at intermediateshipping transload points. It should be noted that to achieve thisbeneficial effect, it is not necessary that all particles within a batch(e.g., a truckload) be coated with the coating composition as describedherein. Rather, in some embodiments, it may be desirable to only coat afraction of the particles, for instance to reduce costs. By way ofexample, it may be desirable to coat 90 weight percent or less of theparticles, alternatively 70 weight percent or less, or alternatively 50weight percent or less. In some embodiments, it may be desirable for atleast 20 weight percent, alternatively at least 30 weight percent, oralternatively at least 40% of the particles in a proppant batch to becoated. The coated particles, however should be blended in with theuncoated particles prior to transport and further handling that mayinduce dust to form.

In some embodiments useful in sub-freezing environments, an anti-freezesolvent may be partially substituted for water in the coatingformulations. The impact of this substitution is to lower the freezingpoint of the emulsion sprayed onto the proppant particle and also toreduce the tendency of the proppant particles to freeze during transportin regions where the average daily temperature is significantly below 0°C. and the proppant has the chance to freeze together.

The antifreeze solvent may include ethylene glycol, diethylene glycol,triethylene glycol, propylene glycol, 1,2-butanediol, methanol, ethanol,propanol, butanol, pentanol, hexanol, heptanol, ethers containing 2 to14 carbon atoms, or ketones containing 2 to 14 carbon atoms.

In some embodiments, the amount of antifreeze solvent used in thecoating formulation may be up to 10 wt %, alternatively up to 20 wt %,alternatively up to 30 wt %, alternatively up to 40 wt %, alternativelyup to 60 wt %, or alternatively up to 80 wt %, based on substitution ofwater.

Some embodiments of the invention will now be described in detail in thefollowing Examples.

EXAMPLES

Polymer Preparation

Suitable polymer binders for use in the examples may be prepared, forinstance, as shown in U.S. Pre-grant publication 2009/0155474, in U.S.Pat. No. 6,214,328, and/or they may be commercially available.

A typical procedure for making polymer is as follows. To a three liter,four-neck round bottom flask quipped with overhead stirrer, condenser,nitrogen adapter and a thermocouple is added 430 parts water, 10.9 partsof benzoic acid, and 19.2 parts of Rhodafac RS-610A (available fromRhodia). Separately, a stage-1 monomer emulsion is prepared by mixing183 parts of water, 6.4 parts of Rhodafac RS-610A, 80 parts of butylacrylate (BA), 200 parts of ethyl acrylate (EA), 60 parts ofhydroxyethyl methacrylate (HEMA), 60 parts of methacrylic acid (MAA),and 4 parts of n-dodecyl mercaptan (n-DDM). With the nitrogen turned on,the reactor and contents at 85 C, 42 part of the above stage-1 monomeremulsion is charged with stirring, followed by an initiator solution of1 part of sodium persulfate dissolved in 15 parts of water. Theremaining monomer emulsion is then fed over 48 minutes, whilemaintaining a temperature of 85 C. A co-feed initiator solutioncontaining 1 part of sodium persulfate and 73 parts of water isgradually added simultaneously with this monomer feed as well as stage 2monomer feed as described later. After stage-1 monomer is completelyfed, stage-2 monomer is prepared by mixing 270 parts of water, 9.6 partsof Rhodafac RS-610A, 150 parts of butyl acrylate (BA), 282 parts ofmethyl methacrylate (MMA), 60 parts of hydroxyethyl methacrylate (HEMA),108 parts of methacrylic acid (MAA), and 1.8 parts of n-dodecylmercaptan (n-DDM). The stage-2 monomer emulsion is fed over 72 minutes,while maintaining a temperature of 85 C.

After the monomer emulsion and initiator feeds are complete, thereaction mixtures are “chased” with a ferrous sulfate, t-butylhydroperoxide, ammonium persulfate, D-isoascorbic acid combination toreduce residual monomer levels. The reaction mixture is then cooled toroom temperature and filtered. The emulsion polymer prepared has solidsof 47%.

A typical procedure for prepare the aqueous coating compositions of theexamples, containing the polymer binder, surfactant, water, and variousoptional ingredients, is as follows.

1. Charge deionized water to kettle. Heat to 60° C. 2. Stir water toestablish and maintain a vortex throughout the process and addflocculant at a slow rate. Continue stirring for 60-120 minutes untilthe solution appears homogeneous. 3. Allow to cool to a temperaturebelow the cloud point of the surfactant. 4. Add surfactant and agitate10 minutes. 5. Add binder and agitate for 10 minutes. 6. Add optionalingredients together or sequentially with intermediate agitation betweenadditions.

Example coating compositions (formulations) that may be preparedaccording to the protocols described above are shown in Tables 1-8.

TABLE 1 Formulation 1 2 3 C₈—C₁₄O—(CH₂CH (CH₃)—O)₂₋₅(CH₂CH₂O)₅₋₉—Hsurfactant at 100% 30 30 0 solidsC₄H₉—CH(C₂H₅)—CH₂—O—(CH₂CH(CH₃)—O)₄₋₆—(CH₂CH₂O)₅₋₇—H 0 0 30 surfactantat 100% solids Polymer binder emulsion derived from 69 to 71 weightpercent of butyl 15 0 0 acrylate; from 27 to 29 weight percent ofstyrene; and from 1 to 3 weight percent of acrylamide at 56% solids inwater Polymer binder emulsion derived from 69 to 71 weight percent ofbutyl 0 15 15 acrylate; from 27 to 29 weight percent of styrene; from0.25 to 0.75 weight percent hydroxyethylmethacrylate; and from 1-3weight percent of acrylamide at 56% solids in water Flocculant: HO—[—CH₂CH₂O—]_(n)—H, where n averages about 80,000 0.02 0.02 0.02 to95,000 at 100% solids Silicone Based Defoamer Foamaster MO 2111,supplied by BASF Corp 1.5 1.5 1.5 at 100% solids. Diluent: Water 53.1753.17 53.17 Preservative: Kathon CG ICP, supplied by The Dow ChemicalCompany 0.31 0.31 0.31 at 1.5% solids in water Total 100.00 100.00100.00

TABLE 2 Formulation 4 5 6 7 8 9 C₈—C₁₄O—(CH₂CH (CH₃)—O)₂₋₅(CH₂CH₂O)₅₋₉—Hsurfactant at 100% 30 30 30 30 0 30 solidsC₄H₉—CH(C₂H₅)—CH₂—O—(CH₂CH(CH₃)—O)₄₋₆—(CH₂CH₂O)₅₋₇—H 0 0 0 0 30 0surfactant at 100% solids Polymer binder emulsion derived from 69 to 71weight percent of butyl 15 15 15 15 15 15 acrylate; from 26 to 28 weightpercent of styrene; from 0.25 to 0.75 weight percenthydroxyethylmethacrylate; and from 1-3 weight percent of acrylamide at56% solids in water Flocculant: HO —[—CH₂CH₂O—]_(n) —H, where n averagesabout 80,000 0.02 0.02 0.02 0.02 0.02 0.02 to 95,000 at 100% solidsSilicone based Defoamer: Foamaster MO 2111 , supplied by BASF Corp. 1.51.5 1.5 3.0 1.5 1.5 at 100% solids Premix Optical Brightener Package Addwith stirring Solvent: 2,2,4-trimethyl-1,3-pentanediolmono(2-methylpropanoate) 0.8 0.8 0.8 0.8 0.8 0.8 Optical Brightener:7-diethylamino-4-methyl coumarin at 100% solids 0.084 0.0008 0.042 0.0420.017 0.017 Add Diluent: Water 53.17 53.17 53.17 51.6 53.17 53.17Preservative: Kathon CG ICP, supplied by the Dow Chemical Company 0.310.31 0.31 0.31 0.31 0.31 at 1.5% solids in water Total 100.88 100.80100.84 100.77 100.82 100.82

TABLE 3 Formulation 10 11 12 13 C₈—C₁₄O—(CH₂CH (CH₃)—O)₂₋₅(CH₂CH₂O)₅₋₉—Hsurfactant at 100% 30 30 30 30 solidsC₄H₉—CH(C₂H₅)—CH₂—O—(CH₂CH(CH₃)—O)₄₋₆—(CH₂CH₂O)₅₋₇—H 0 0 0 0 surfactantat 100% solids Polymer binder emulsion derived from 69 to 71 weightpercent of butyl 15 15 15 15 acrylate; from 27 to 29 weight percent ofstyrene; from 0.25 to 0.75 weight percent hydroxyethylmethacrylate; andfrom 1-3 weight percent of acrylamide at 56% solids in water Flocculant:HO —[—CH₂CH₂O—]_(n) —H, where n averages about 80,000 to 0.02 0.02 0.020.02 95,000 at 100% solids Silicone Defoamer: Foamaster MO 2111 ,supplied by BASF Corp. at 1.5 1.5 3.0 1.5 100% solids Premix OpticalBrightener Package Add with stirring Solvent:2,2,4-trimethy1-1,3-pentanediol diisobutyrate 0.8 Solvent:1,2-Benzenedicarboxylic acid dibutyl ester 0.8 0.8 Solvent:2,2,4-trimethy1-1,3-pentanediol mono(2-methylpropanoate) 0.8 OpticalBrightener: 7-diethylamino-4-methyl coumarin at 100% solids 0.084 0.0080.042 0.042 Add Diluent: Water 53.17 53.17 53.17 51.6 Preservative:Kathon CG ICP, supplied by the Dow Chemical Company 0.31 0.31 0.31 0.31at 1.5% solids in water Total 100.88 100.81 102.34 99.27

TABLE 4 Formulation 14 15 16 17 18 19 20 C₈—C₁₄O—(CH₂CH(CH₃)—O)₂₋₅(CH₂CH₂O)₅₋₉—H 0 0 0 0 0 30 30 surfactant at 100% solidsC₄H₉—CH(C₂H₅)—CH₂—O—(CH₂CH(CH₃)—O)₄₋₆— 30 30 30 30 30 0 0 (CH₂CH₂O)₅₋₇—Hsurfactant at 100% solids Polymer Binder emulsion derived from 2 stages.15 Stage 1 19-21 weight percent butyl acrylate; 49-51 weight percentethyl acrylate; 14-16 weight percent hydroxyethyl methacrylate and 14-16weight percent methacrylic acid. Stage 2 24-26 weight percent butylacrylate; 46-48 weight percent methyl methacrylate; 9-11 weight percenthydroxyethyl methacrylate and 17-19 weight percent methacrylic acid. At46% solids in water. Polymer binder emulsion derived from 27 to 29 15weight percent of butyl acrylate; from 61 to 63 weight percent of methylmethacrylate; and from 9 to 11 weight percent of methacrylic acid,crosslinked with zinc ion (about 0.5 equivalents). At 38% solids inwater. Polymer Binder emulsion derived from 59-61 15 weight percentStyrene 39-41 weight percent butadiene. At 48% solids in water. Polymerbinder emulsion derived from 39 to 41 15 15 weight percent of styrene;from 29 to 31 weight percent of butyl acrylate; from 15 to 17 weightpercent of methyl methacrylate; from 4 to 6 weight percent Hydroxyethylmethacrylate; from 4 to 6 weight percent acrylic acid; and from 4 to 6weight percent of methacrylic acid, crosslinked with zinc ion (about 0.9equivalents). At 38% solids in water. Polymer binder emulsion derivedfrom 69 to 71 15 15 weight percent of butyl acrylate; from 27 to 29weight percent of styrene; from 0.25 to 0.75 weight percenthydroxyethylmethacrylate; and from 1-3 weight percent of acrylamide at56% solids in water Flocculant: HO —[—CH₂CH₂O—]_(n)—H, where n 0.02 0.020.02 0.02 0.02 0.02 0.02 averages about 80,000 to 95,000 at 100% solidsSilicone Defoamer: Foamaster MO 2111, 3 3 3 3 3 3 3 supplied by BASFCorp. at 100% solids Premix Optical Brightener Package Add with stirringSolvent: 2,2,4-trimethyl-1,3-pentanediol mono(2- 0.8 0.8 0.8 0.8 0.8 0.80.8 methylpropanoate) Optical Brightener: 7-diethylamino-4-methyl 0.0420.042 0.042 0.042 0 coumarin at 100% solids Optical Brightener2,2′-[(1,1′-BIPHENYL)-4,4′- 0.042 DIYLDI-2,1-ETHENEDIYL]-BIS-BENZENESULFONIC ACID DISODIUM SALT OpticalBrightener2,5-Bis(5-tert-butyl-benzoxazol- 0.042 2-yl)thiophene AddDiluent: Water 51.17 51.17 51.17 51.17 51.17 51.17 51.17 Preservative:Kathon CG ICP, supplied by the 0.31 0.31 0.31 0.31 0.31 0.31 0.31 DowChemical Company at 1.5% solids in water Total 100.34 100.34 100.34100.34 100.34 100.34 100.30

TABLE 5 Formulation 21 22 23 CH₃(CH₂)₁₀CH₂(OCH₂CH₂)₂₋₄OSO₃Na. 30 0 0surfactant at 30% solids NaSO₃—C6H₅—O—C₆H₄(C₁₂H₂₆)SO₃Na 0 30 0surfactant at 45% solids [C₅H₅O(OH)₄]₁₋₃—O—C₈H₁₇—C₁₄H₂₉ 30 surfactant at51% solids Polymer binder emulsion derived from 69 to 15 0 0 71 weightpercent of butyl acrylate; from 27 to 29 weight percent of styrene; andfrom 1 to 3 weight percent of acrylamide at 56% solids in water Polymerbinder emulsion derived from 69 to 0 15 15 71 weight percent of butylacrylate; from 27 to 29 weight percent of styrene; from 0.25 to 0.75weight percent hydroxyethylmethacrylate; and from 1-3 weight percent ofacrylamide at 56% solids in water Flocculant: HO —[—CH₂CH₂O—]_(n)—H,0.02 0.02 0.02 where n averages about 80,000 to 95,000 at 100% solidsSilicone Based Defoamer Foamaster MO 1.5 1.5 1.5 2111, supplied by BASFCorp at 100% solids. Diluent: Water 53.17 53.17 53.17 Preservative:Kathon CG ICP, supplied by 0.31 0.31 0.31 The Dow Chemical Company at1.5% solids in water Total (grams) 100.00 100.00 100.00

TABLE 6 Formulation 24 25 C₈—C₁₄O—(CH₂CH (CH₃)—O)₂₋₅(CH₂CH₂O)₅₋₉—H 4 0surfactant at 100% solids Polymer binder emulsion derived from 69 to 71weight 0 7.14 percent of butyl acrylate; from 27 to 29 weight percent ofstyrene; from 0.25 to 0.75 weight percent hydroxyethylmethacrylate; andfrom 1-3 weight percent of acrylamide at 56% solids in water Diluent:Water 16 12.86 Total (grams) 20 20

TABLE 7 Formulation 26 27 28 29 Polymer binder emulsion derived from 69to 71 weight percent 15 15 15 15 of butyl acrylate; from 27 to 29 weightpercent of styrene; from 0.25 to 0.75 weight percenthydroxyethylmethacrylate; and from 1-3 weight percent of acrylamide at56% solids in water C₈—C₁₄O—(CH₂CH (CH₃)—O)₂₋₅(CH₂CH₂O)₅₋₉—H 0 0 0 0surfactant at 100% solids CH₃(CH₂)₁₄CH₂—N—(CH₃)₃Cl surfactant at 25%solids 60 0 0 0 CH₃(CH₂)₁₀CH₂(OCH₂CH₂)₂₋₄ OSO₃Na. surfactant at 30% 0 500 0 solids NaSO₃—C6H₅—O—C₆H₄(C₁₂H₂₆)SO₃Na surfactant at 45% 0 0 50 0solids [C₅H₅O(OH)₄]₁₋₃—O—C₈H₁₇—C₁₄H₂₉ Surfactant at 51% 0 0 0 29.41solids Silicone Based Defoamer Foamaster MO 2111, supplied by 1.5 1.51.5 1.5 BASF Corp at 100% solids. Water 23.5 33.5 33.5 54.09 Total(grams) 100.0 100.0 100.0 100.0

TABLE 8 Formulation 30 31 Polymer binder emulsion derived from 69 to 71weight percent of butyl 15 15 acrylate; from 27 to 29 weight percent ofstyrene; from 0.25 to 0.75 weight percent hydroxyethylmethacrylate; andfrom 1-3 weight percent of acrylamide at 56% solids in waterC₃H₇CHO(C₂H₄O)₄₋₆C₂H₄(CH₂)₄₋₆CH₃ surfactant at 100% solids 15 0C₄H₉—CH(C₂H₅)—CH₂—O—(CH₂CH(CH₃)—O)₄₋₆—(CH₂CH₂O)₈₋₁₀—H 15 0 surfactant at100% solids C₃H₇CHO(C₂H₄O)₆₋₈C₂H₄(CH₂)₄₋₆CH₃ surfactant at 100% solids 015 C₄H₉—CH(C₂H₅)—CH₂—O—(CH₂CH(CH₃)—O)₄₋₆—(CH₂CH₂O)₅₋₇—H 0 15 surfactantat 100% solids Premix Optical Brightener Package Optical Brightener:7-diethylamino-4-methyl coumarin at 100% solids 0.042 0.042 Solvent:2,2,4-trimethyl-1,3-pentanediol mono(2-methylpropanoate) 0.8 0.8 AddSilicone Based Defoamer Foamaster MO 2111, supplied by BASF Corp at 1.51.5 100% solids. Solvent: propylene glycol 5 31.33 Water 47.66 21.33Total (grams) 100.00 100.00

Various of the aqueous compositions shown in the above Tables areapplied to sand particles and their properties evaluation underdifferent test conditions. Comparisons are made to untreated sandparticles (comparative examples).

Procedure for Analyzing Particle Size: LS 13 320 Laser DiffractionParticle Size Analyzer

The Beckman Coulter LS 13 320 will measure the size distribution ofparticles suspended either in a liquid or in dry powder form by usingthe principles of light scattering. This instrument is composed of theLS 13 320 optical bench and an Aqueous Liquid Module (ALM). Thisinstrument utilizes PIDS (Polarization Intensity DifferentialScattering) enabling a dynamic measurement range of 0.04 to 2000 micron.The method involves the analysis (deconvolution) of the patterns ofscattered light produced when particles of different sizes are exposedto a beam of light. The LS 13 320 series of instruments takes advantageof these principle to rapidly provide precise and reproducible particlesize distributions.

The Tornado Dry Powder System is intended for use with the LS 13 320Optical Bench. It is capable of feeding and measuring dry powder samplesin the size range 0.4 μm to 2000 μm. The Tornado DPS measures the entiresample presented to the instrument, with a sample volume that allows ananalysis that will provide statistically accurate results. The range ofsample volumes the instrument can accept should provide for a minimum 10second run at controlled obscuration. The sample is placed in a sampleholder and delivered to the sensing zone in the optical bench by avacuum. The Tornado DPS provides automatic feed rate (obscuration)control. The set point for the obscuration is user selectable between 4%and 8%. The accuracy of the average obscuration control is better than±2% from the set point.

The system disperses cohesive powders without milling fragile materials.The dispersion of the dry powders is comparable to the dispersionachieved when the samples are run wet with proper manual pre-dispersion.The sample to be measured is contained in the system to prevent airbornecontamination of the work area throughout. This is accomplished bymaintaining a negative pressure (vacuum) system for the sample path andtrapping the sample via a filtration system in the vacuum.

In an exemplary procedure, proppant Sand (20/40 mesh) is ground in aOsterizer 14 speed Blender set at “Liquefy” (highest setting) for 2minutes to produce fines, alternatively the Proppant sand (20/40 mesh)is placed in a ceramic jar with ceramic one inch diameter balls andplaced on a roller mill overnight to produce fines to mimic fines ordust that are produced during pneumatic conveyance of the sand duringtransloading operations at a proppant transportation site.

Preweighed sand is placed into a stack of U.S. Standard Sieve Serieswith Lid and pan. Screen Mesh series No. 20, 40, 100, corresponding to840, 420 and 150 microns. Sieve set placed on Sieve shaker for 15minutes to separate the sand sizes. From each sieve, the resulting sandis re-weighed and the fractions collected separately. Depending on theparticle size range of interest, sand as contained can range from150-840 microns or larger, sieved sand can be distinct ranges. The sandis preweighed into jars, starting at 65 grams. To obtain a reading onthe untreated sand, 5 grams is removed and the particle sizedistribution and volume fraction is determined using the Beckman LS 13320 Tornando attachment. For the remaining 60 grams of sand, 0.15 gramsof formulation is sprayed or dispensed onto the sand, with resultingtreatment of 0.05%. A Sequest Perfect Euromist Optima (160 microliter)0.014″×0.010″ deep, 0.060′ tubing internal diameter pump valve fromAptar Group, Il, USA is used as the spray device. The spray device isfitted to a 60 ml plastic polyethylene container designed to accommodatethe device. Formulations to be tested are charged to the 60 ml containerto dispense by the sprayer onto the sand. If other rates of applicationare required, the amount of formulation is adjusted to achieve thedesired amount deposited to the sand. Additionally, the solids of theformulation are taken into account to deposit the targeted amount ofcoating to the sand. Formulations are applied based on a solids basis.The jar is capped and the sand with the formulation is vigorously shakenor for 2 minutes. Aliquots of the formula treated sand are tested on theBeckman LS 13320 Tornado, with up to 10 replicates.

Particle Size Range from 150 to 420 Microns (Formulation 6 vs Untreated)

Sand supplied at 20/40 mesh (840 to 420 microns) was stressed orfractured in the roller mill or blender to produce fines or dustparticles to mimic the dust produced during proppant conveyance. Therange in sieves 100/40 produces a micron range of 150 to 420 used inthis study.

A common approach to define the distribution width from the BeckmanCoulter Particle size analyzer is to cite five values on the x-axis; theD<10%, D<25%, D<50%, D<75% and D<90% as depicted in the tables below.The D,50%, known as the median, has been defined as the diameter wherehalf the population of particles lies below this value. Similarly, D<90%defines the distribution that lies below this diameter and D<10% isindicative of 10% of the population below that diameter. Data comparingsand coated with inventive formulation 6 versus untreated sand(comparative) is in Table 9.

TABLE 9 Microns Formulation/Treatment <10% <25% <50% <75% <90% 6 292 3603663 457 533 No Treatment 192 246 338 440 523Particle Size shift. Data shows treatment with formulation 6 shifts theparticle size distribution to higher particle sizes. This corresponds toless dust or finer particles present in field operations where proppantsare being handled.Particle Size Range from 150-420 Microns Particle (Formulation 2 vsUntreated)

Sand supplied at 20/40 mesh (840 to 420 microns) was stressed orfractured in the roller mill or blender to produce fines or dustparticles to mimic the dust produced during proppant conveyance. Therange in sieves 100/40 produces a micron range of 150 to 420 used inthis study. Data comparing sand coated with inventive formulation 2versus untreated sand (comparative) is in Table 10.

TABLE 10 Microns Formulation/Treatment <10% <25% <50% <75% <90% 2 212279 377 468 530 No Treatment 202 261 357 453 533Particle Size shift. Data show treatment with formulation 2 shifting theparticle size distribution to higher sizes. This corresponds to lessdust or finer particles present in field operations where proppants arebeing handled.500 ppm of coating on sand (sprayed) 20/40 sand. Particle size range 150microns to 850 microns (formulations 1, 2, and 3 vs untreated)

Data comparing sand coated with inventive formulations versus untreatedsand (comparative) is in Table 11.

TABLE 11 Microns Sample <10% <25% <50% <75% <90% Untreated 493 594 696803 903 1 514 606 705 805 906 2 502 597 697 804 905 3 529 613 713 824927Particle Size shift. Data show treatment shifting the particle sizedistribution to higher sizes. This corresponds to less dust or finerparticles present in field operations where proppants are being handled.500 ppm of coating on sand (sprayed) 20/40 sand. Particle size range 150microns to 850 microns (formulations 1, 2, 4, and 5 vs untreated)

Data comparing sand coated with inventive formulations versus untreatedsand (comparative) is in Table 12.

TABLE 12 Microns Sample <10% <25% <50% <75% <90% Untreated 514 609 710813 913 1 528 622 735 883 1026 2 458 571 718 917 1092 4 535 626 727 834938 5 551 634 734 844 954Data in the table shows treatments providing larger particles, hencesuppressing the finer particles being generated during the grinding ofthe sand.500 ppm of coating on sand (sprayed) 20/40 sand. Particle size range 150microns to 850 microns (formulations 2, 7, 14, 15, 16, 18, 19, and 20 vsuntreated)

Data comparing sand coated with inventive formulations versus untreatedsand (comparative) is in Table 13 and 14.

TABLE 13 <10% <25% <50% <75% <90% Sample (μm) (μm) (μm) (μm) (μm)Untreated 481.3 559.8 664.4 812.0 982.7 2 379.0 554.9 958.4 1354.11490.2 Untreated 457.0 552.2 654.7 779.2 901.5 7 494.6 579.9 681.0 786.41048.3 Untreated 545.7 620.3 724.4 845.1 950.9 14 520.8 631.2 727.8824.6 1107.3 Untreated 523.7 596.5 696.7 812.4 920.4 15 518.3 612.8709.0 801.3 984.5

TABLE 14 <10% <25% <50% <75% <90% Sample (μm) (μm) (μm) (μm) (μm)Untreated 496.0 533.4 675.9 870.4 1185.0 Formulation #2 504.0 582.5709.5 989.6 1679.0 Untreated 515.7 581.4 711.6 899.2 1176.0 Formulation#7 520.0 570.1 719.8 803.7 1640.7 Untreated 541.8 593.5 690.6 801.2902.8 Formulation #16 515.2 571.3 682.6 768.2 1112.8 Untreated 465.9545.5 647.5 816.0 990.5 Formulation #18 516.9 573.3 667.6 757.8 927.7Untreated 510.1 578.9 706.5 873.6 1047.0 Formulation #19 469.8 581.6773.9 883.5 1182.9 Untreated 477.7 544.2 640.0 794.1 1006.0 Formulation#20 535.8 589.1 688.8 791.0 887.2Particle Size shift. Data show treatment shifting the particle sizedistribution to higher sizes. This corresponds to less dust or finerparticles present in field operations where proppants are being handled.

An alternative approach to analyzing the particle size suppression is tocalculate the area under the curve and compare untreated sand to sandtreated with the formulations. A reduction of area under the curvecorresponds to a recution in fines or dust during the proppantconveyance. Such data is shown in FIG. 1.

500 ppm of coating on sand (sprayed) 20/40 sand. Particle size rangeless than 150 microns.

For this study, Sand originally supplied at 20/40 mesh (840/420 microns)was stressed to produce a particle size range less than 150 microns tomimic the fines or dust generated during proppant conveyance. Data areshown in Table 15.

TABLE 15 % Reduction in Area Formulation Area Under the Curve vsUntreated 2 590.1 5.3 13 425.3 31.7 7 92.3 85.2 11 173 72.2 10 117.781.1Dust Suppression Showing Different Coating Compositions of thisInvention

Sand supplied at 20/40 mesh (840 to 420 microns) was stressed orfractured in the roller mill or blender to produce fines or dustparticles to mimic the dust produced during proppant conveyance. Therange in sieves 100/40 produces a micron range of 150 to 850 used inthis study. Formulations were applied by spray application to obtain thedesired coating amount. Data is shown in Table 16.

TABLE 16 Formulation Formulation Formulation Sample untreated 21 22 23Coating No 500 parts 500 parts 500 parts Application Application permillion per million per million rate Area 6882 6598 6632 6771Application rate designates the amount of material applied to coating ona solids basisDemonstrates that Individual Components not as Effective as Combination.

In the following examples, the Beckman Coulter LS 13 320 fitted with theTornado Dry Powder System was used to determine particle characteristicsof sand coated with the formulations. The total area of the particledistribution (0-2000 microns) measured by the Beckman Coulter LS 1320fitted with the Tornado Dry Powder System was determined by output fromthe device. The area represents an integrated measurement of ameasurable effect or phenomenon of the volume percent of particles atthe different particle sizes determined during the measurement. It isused as a cumulative measurement of particle size distribution. Anoverall reduction in the measurement (area), in this case particle sizeunder a defined range of sizes is associated with an overall reductionof the particles or dust.

Sand supplied at 20/40 mesh (840 to 420 microns) was stressed orfractured in the roller mill or blender to produce fines or dustparticles to mimic the dust produced during proppant conveyance. Therange in sieves 100/40 produces a micron range of 150 to 850 used inthis study. Formulations were applied by spray application to obtain thedesired coating amount.

TABLE 17 Sample Formulation 2 Formulation 24 Formulation 25 Amount(parts 500 500 500 per million) Area 6162 6802 6759The lower area value of Formulation 2 compared to Formulation 24 andFormulation 25 show less particles being generated in the Tornado DryPowder System. The higher area values for Formulation 24 (surfactantonly) formulation and Formulation 25 (polymer only) formulation indicatemore dust particles being generated in the Tornado Dry Powder System.The data shows that the combination of the surfactant and the polymerdemonstrates the dust suppression of proppant dust of the inventionbetter than the individual components, separately.Turbidity Readings

Yet another approach to analyzing the particle suppression provided bythe compositions of the invention is to determine the suspension ofparticles in water extractions from coated and uncoated sand bymeasuring the turbidity of the water extractions. Turbidity is measuredby an instrument called a nephelometer. The units of turbidity from anephelometer are Nephelometric Turbidity Units (NTU). High NTU valuesindicate higher turbidity and lower NTU values indicate lower turbidity.Turbidity in the water extractions of the coated and uncoated sand isdue to particles suspended in the water. Low NTU values of the coatedsand indicate that less particles are extracted from the coated sanddemonstrating particle dust suppression. The uncoated sand has thehighest NTU value indicating more particles being extracted from thesand.

Sand Turbidity Method

Sample Preparation:

Sand coating information should be obtained from sand source or recordedduring preparation including sand sieve size and experimental ppmcoating level (calculated using weight of formulation added to sand,sand weight, and formulation solids content). At higher sand coatinglevels, a pronounced effect of formulation leaving the sand anddissolving into the water will affect readings as the test solution canbecome an opaque white. For the current invention, small aliquots ofsand (˜20 g each) are placed in a weighing tin. The sand is spreadacross the weighing tin and dried at 80 degrees Celsius overnight to dryand adhere the coating to the sand to avoid this noise.Oakton T-100 Turbidity Meter (Nephelometer)—Instrument Calibration:The Oakton T-100 Turbidity meter should be powered up and calibratedshortly prior to use. By pressing the CAL button, the standards can beentered in descending turbidity. Wait for the instrument to display thecurrent standard to be read, ensure the outside of the test vial isclean with a kimwipe, place the vial in the holder with the arrows onvial and reader aligned, and press enter. The order of reading shouldbe: 800 (NTUs), 100, 20, and 0.02. Before reading test samples it issuggested that the standard closest to the expected turbidity values forthe samples be read to check the accuracy of the calibration.Testing Samples:Weigh 3 grams±0.03 g on analytical balance and record weight. Usemicropipette to add 15 mL of DI water to vial. Agitate sample using aVortex mixer for 5 seconds (start time from when sample reaches mixingvelocity, the samples take a moment to speed up). Immediately remove 10mL from the top of the vial using the micropipette and taking care notto draw up sand into the clean pipette tip. Dispense into turbidity readvial. Immediately prior to reading, invert vial gently 3 times, placevial in holder and align the arrows, set timer for 60 seconds and readat end of time period. Repeat for additional samples using clean vialsand pipette tips. A background sample test of deionized water issuggested to ensure any detectable level of turbidity from the wateritself or minute amounts from cleaning the vial are noted and subtractedfrom the test samples.Demonstrates Range of Coating Weights Applied to Sand.

For this study, Sand having a 40/70 mesh (420/210 microns) was used assupplied and treated with Formulation 2 composition of this invention todetermine fines or dust suppression that would be indicative duringproppant conveyance. The coatings were applied by spray application aspreviously described and adjusting for the amount of coating to beapplied to obtain the desired rate of coating application on a solidsbasis as provided in Table 18.

TABLE 18 Coating Amount (parts per million) 0 125 250 500 1000 2000 NTU22.1 8.03 4.61 4.11 3.43 2.41 Note: NTU represents average of threedeterminations

For the following study, Sand having a 40/70 mesh (420/210 microns) wasused as supplied and treated with the compositions of this invention todetermine fines or dust suppression that would be indicative duringproppant conveyance. The coatings were applied by spray application aspreviously described with a 500 ppm amount of coating being applied toon a solids basis. Data are shown in Table 19 and demonstrate lowerturbidity values for the compositions of the invention, corresponding toreduced dust.

TABLE 19 Formu- Formu- Formu- Formu- Sample uncoated lation 26 lation 27lation 28 lation 29 NTU 24.13 2.77 5.36 5.96 3.96 valueDust Suppression Using Surfactant Blends

Sand supplied at 20/40 mesh (840 to 420 microns) was stressed orfractured in the roller mill or blender to produce fines or dustparticles to mimic the dust produced during proppant conveyance. Therange in sieves 100/40 produces a micron range of 150 to 850 used inthis study. 500 parts per million of coating on a solids basis wasapplied to the sand and the area of the particle distribution wasmeasured. The Beckman Coulter LS 13 320 fitted with the Tornado DryPowder System was used to measure the particle distribution in the0-2000 micron range and obtain the area measurements. Data are shown inTable 20.

Table 20.

TABLE 20 Sample Untreated Formulation 30 Formulation 31 Area 7269.556618.02 6778.66The untreated sand showed more dust as measured by the larger areadetermined from the instrument. The treated sand with coatings of thisinvention, Formulation 32 and Formulation 33, showed lower areaindicating less dust. The instrument detects less dust in the TornadoChamber and this is reflected in a lower area being measured for theparticle distribution detected by the instrument.

What is claimed is:
 1. A proppant for use in hydraulic fracturing,comprising: a particle; and a coating disposed on the particle that isformed from an aqueous coating composition, the aqueous coatingcomposition comprising, based on the total weight of the aqueous coatingcomposition, from 2 to 65 weight percent of a surfactant, from 1 to 35weight percent of a polymer binder that is a water insoluble emulsionpolymer, and balance water, the polymer binder comprising an aqueousdispersion of particles made from a copolymer, based on the weight ofthe copolymer, comprising: i) from 90 to 99.9 weight percent of at leastone ethylenically unsaturated monomer not including component ii; andii) from 0.1 to 10 weight percent of (meth)acrylamide.
 2. The proppantof claim 1 wherein the surfactant is an alkoxylate.
 3. The proppant ofclaim 1 wherein the coating further comprises an optical brightener. 4.The proppant of claim 3 wherein the optical brightener is coumarin or acoumarin derivative, a bis-stilbene compound, a bis(benzoxazolyl)thiophene compound, a 4,4′-bis(2-benzoxazolyl)stilbene compound, or amixture of two or more thereof.
 5. The proppant of claim 1 wherein thecoating further comprises an anti-freeze solvent.
 6. A process formaking the proppant of claim 1 comprising blending in a mixer withmechanical agitation the particle and the aqueous coating composition;or by spraying the aqueous coating composition onto a moving bed or afalling stream of the particles.
 7. A method for reducing dustgeneration associated with hydraulic fracturing operations, the methodcomprising using the proppant of claim
 1. 8. The method of claim 7wherein the hydraulic fracturing operation is transloading, conveying oroffloading of the proppant at a wellsite and/or at intermediate shippingtransload points.
 9. The proppant of claim 1 wherein the coating coversless than 50 percent of the particle.
 10. The proppant of claim 1wherein the aqueous coating composition comprises from 5 to 50 weightpercent of the surfactant and from 5 to 20 weight percent of the polymerbinder, based on the total weight of the aqueous coating composition.11. The proppant of claim 1 wherein the surfactant is a nonionicalkoxylate surfactant and the polymer binder is derived from butylacrylate, styrene, (meth)acrylamide, and optionally hydroxyethylmethacrylate.
 12. The proppant of claim 1 wherein an amount of coatingon the particle, on a dry basis, is between 300 ppm and 700 ppm ofparticle weight.